Nanoporous Polybenzoxazine Aerogels for Thermally Insulating and Self-Extinguishing Materials in Aerospace Applications

Phenolic-based
aerogel composites possess particular characteristics,
such as low thermal conductivity, light weight, and superior ablative
properties, in near-space vehicles. However, their machinability and
flammability require further improvement, hampering their application
for high-performance thermal protection systems in the aerospace field.
Here, we prepare nanoporous polybenzoxazine (PBO) aerogels with outstanding
thermally insulating and self-extinguishing properties by an effective-cost
ambient pressure drying (APD) approach rather than a conventional
high-pressure supercritical drying pattern. The PBO aerogels are prepared
by adopting different exchange solvents of tert-butyl
alcohol, ethanol, and n-hexane. The results obtained
indicate that PBO aerogels (with n-hexane as the
exchange solvent) by APD have an optimal three-dimensional nanoporous
network structure, a pore size distribution in the range 20–140
nm, an obvious self-extinguishing property (extinguished itself instantly
despite exposure to a 1200 °C flame), superior thermal insulation
(the cold surface temperature of the sample reached only 36.4 °C
after 400 s despite its opposite surface existing at a 65.8 °C
atmosphere), and excellent machinable properties (easy-to-form special-shaped
sample). PBO aerogels are a great potential candidate material system
for thermal protection systems in aerospace applications in the future.